(19)
(11) EP 0 780 695 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
21.01.1998 Bulletin 1998/04

(43) Date of publication A2:
25.06.1997 Bulletin 1997/26

(21) Application number: 96309328.1

(22) Date of filing: 18.12.1996
(51) International Patent Classification (IPC)6G01R 31/28, G01R 1/20
(84) Designated Contracting States:
DE FR GB

(30) Priority: 21.12.1995 US 576008

(71) Applicant: GENRAD, INC.
Concord Massachusetts 01742 (US)

(72) Inventors:
  • Pye, Richard
    Waltham, Massachusetts 02154 (US)
  • Khazam, Moses
    Lexington, Massachusetts 02173 (US)

(74) Representative: Waldren, Robin Michael 
MARKS & CLERK, 57-60 Lincoln's Inn Fields
London WC2A 3LS
London WC2A 3LS (GB)

   


(54) Hybrid scanner for use in a tester


(57) A hybrid scanner for switching internal analog buses to system pin channels. Semiconductor switches switch most scanner buses to system pin channels, but mechanical relays perform switching for at least one bus used for high-current test signals. To perform low-impedance guarding and/or high-current backdriving, the low impedance, high current bus is typically connectable to one or more overdriver circuits and a guard voltage potential through mechanical relays. The scanner is capable of supporting in-circuit tests covering the most significant regions of the fault spectrum can be made more reliable and much smaller and less costly than the scanners conventionally used in traditional broad spectrum testers. It turns out that this test-supporting capability can be achieved by adding only a few mechanical relays to an otherwise semiconductor-switch-based scanner. Only those necessary to support low-impedance and high-current test operations.





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